1. Field of the Invention
The invention relates generally to casting and more particularly to a mold for casting cylinder blocks of combustion engines.
2. Description of the Prior Art
Cylinder blocks are normally made of grey cast iron or aluminum alloys. With grey cast iron, the external contours of the cylinder block are formed by a mold of compacted molding sand (e.g. green sand comprising silica sand, bonding clay, namely bentonite, coal dust and water). The internal contours of the cylinder block are formed by means of suitable cores which are made of silica or other types of sand and a cold or hot setting binder system (resin and catalyst). The cores used in such a casting process are very expensive.
There are two types of such molds in use. The most common mold is designed to form a laterally arranged cylinder block through the use of a cope and drag. The aforesaid cores are assembled into the cope and drag which are then joined to ready the mold for casting. The mold is stripped in a direction perpendicular to the axes of the cylinder bores.
With the other mold, the cylinder blocks are cast standing upright on the base area using the aforesaid cores to form the internal contours. The mold halves, which in this particular case are laterally arranged, are also stripped in a direction perpendicular to the axes of the cylinder bores.
The demands of the automobile industry created by the pursuit of weight reduction have resulted in the need for keeping much closer casting tolerances. Unfortunately, the aforesaid casting methods both have the following disadvantages.
The distance deviations between the cope and drag are entirely transferred to a complete block half thus yielding castings with different wall thicknesses and weight differences.
The crank space of the cylinder block is formed by means of a crank space core which is considerably more expensive than the green sand used in the remainder of the mold.
It is difficult to compensate for lifting forces which develop especially in the water-jacket region during the mold filling process.
The methods are necessarily core-intensive which leads to extensive gas production during casting and solidification.